Laser processing method and laser processing apparatus

ABSTRACT

A device-forming region where a semiconductor device is formed is arranged on a substrate in the matrix of 2×2. A linear laser beam has a cross-section having a length longer than the width of the device-forming region. When the irradiation of the laser beam is performed, the region irradiated with the end portions of the linear laser beams overlapped with each other or brought into contact with each other, is made positioned outside the device-forming region.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a laser processing method and alaser processing apparatus, and particularly, to an improvement of athroughput in an optical annealing step with respect to the manufactureof an insulated gate type semiconductor device such as a thin-filmtransistor (TFT) which is formed on a substrate having a crystallinesilicon film of non-single crystal and other semiconductor devices.

[0002] Particularly, the present invention relates to-the manufacture ofa semiconductor device which is formed on an insulating substrate madeof glass or the like and having a large area.

[0003] Recently, studies have been made of an insulated gate typesemiconductor device including a thin-film like active layer (alsoreferred to as active region) on an insulating substrate. Particularly,studies have been made earnestly of thin-film like gate transistors,so-called thin-film transistors (TFT). These transistors are classifiedby the material and crystalline state of a used semiconductor into anamorphous silicon TFT, a crystalline silicon TFT, and the like. Thecrystalline silicon is not a single crystal but a non-single crystal.Accordingly, the general term for these transistors is a non-singlecrystal TFT.

[0004] In general, the mobility of an amorphous semiconductor is small,so that it can not be used as a TFT which is required high spedoperation. Further, since the mobility of a P-type amorphous silicon isextremely small, thereby being unable to manufacture a P-channel TFT(TFT of PMOS) so that it is impossible to form a complementary MOScircuit (CMOS) by combining the P-channel TFT with an N-channel TFT (TFTof NMOS).

[0005] On the other hand, the crystalline semiconductor has a mobilitylarger than that of the amorphous semiconductor, so that high speedoperation can be achieved. By the crystalline silicon, not only TFT ofNMOS but also TFT of PMOS can be obtained, so that it is possible toform a CMOS circuit.

[0006] The crystalline silicon film of non-single crystal has beenobtained by thermally annealing an amorphous silicon film obtained by avapor phase deposition method for a long time at an appropriatetemperature (normally more than 600° C.) or by irradiating it with theintense light such as a laser beam (optical annealing).

[0007] However, in the case where a glass substrate which is cheap andrich in workability, is used as an insulating substrate, it has beenextremely difficult to obtain the crystalline silicon having asufficiently high mobility (so high that a CMOS circuit can be formed)by only the thermal annealing. This is because the above-mentioned glasssubstrate has generally a low distortion point temperature (about 600°C.), so that it is impossible to increase the substrate temperature upto a temperature required to form the crystalline silicon film havingthe sufficiently high mobility.

[0008] On the other hand, in the case where the optical annealing isused to crystallize a silicon film based on a glass substrate, it ispossible to give a high energy to only the silicon film withoutincreasing the substrate temperature to a very high temperature. Thus,the optical annealing technique is regarded as very effective forcrystallizing the silicon film based on the glass substrate.

[0009] At present, a high power pulse laser such as an excimer laser ismost preferable as an optical source for the optical annealing. Themaximum energy of this laser is very large as compared with acontinuous-wave laser such as an argon ion laser, so that it has beenpossible to improve the throughput by using a large spot of more thanseveral cm². However, when a normally used square or rectangular beam isused, it must moved up and down and right and left to process onesubstrate having a large area. Thus, there is a room for improvementfrom the viewpoint of the throughput.

[0010] Concerning this, much improvement has been obtained bytransforming a beam into a liner beam to extend the length of the beam(largeness of the cross section of the linear beam in longitudinaldirection) over a substrate to be processed, and by moving this beamrelatively to the substrate to scan. Here, the scanning means thatirradiation of the laser beam is performed while the linear laser beamis moved in the line width direction (direction orthogonal to thelongitudinal direction of the cross section of the linear beam), and theirradiated regions are overlapped with each other not to separate theirradiated regions. Also, in general, when the irradiation of the linearlaser beam is performed for a large area, the scanning paths are madeparallel to each other.

[0011] Further, before the optical annealing, when the thermal annealingis carried out, it is possible to form a silicon film having moresuperior crystallinity. With respect to the method of the thermalannealing, as disclosed in Japanese Patent Unexamined Publication No.Hei. 6-244104, by using the effect that an element such as nickel, iron,cobalt, platinum, or palladium (hereinafter referred to ascrystallization catalytic element or simply referred to as catalyticelement) accelerates the crystallization of amorphous silicon, thecrystalline silicone film can he obtained by the thermal annealing at alower temperature for a shorter time than a normal case.

[0012] However, in the above irradiation of the linear laser, inrelation to the maximum energy thereof, the length of the linear laserbeam (largeness of the cross section of the laser beam in thelongitudinal direction) has been limited to about 20 cm at best.

[0013] If the processing is performed by the linear laser beam having alength longer than the limit, the energy density of the laser beambecomes insufficient to, for example, crystallize the amorphous siliconfilm. Thus, when a substrate having a large area is used and laserprocessing is performed for a region longer than the length of a linearlaser beam, it has been necessary to perform scanning of the laser beamup and down and left and right, that is, both in the line widthdirection and in the longitudinal direction. FIG. 13(B) schematicallyshows scanning paths of a conventional laser beam.

[0014]FIG. 13(A) is a sectional view of a linear laser beam, and FIG.13(B) is a view showing a surface to be irradiated viewed from theabove. As shown in FIG. 13(A), an end portion 1 a of a linear laser beam1 is not completely rectangular, and the energy density in this portionis dispersed.

[0015] As shown in FIG. 13(B), the scanning of the linear laser beam 1is performed along two scanning paths 2 and 3. For example, after thedownward scanning of the linear laser beam 1 is performed along the leftscanning path 2, the downward scanning is performed along the rightscanning path 3. At this time, it is necessary to perform scanning sothat the end portions 1 a of the linear laser beams 1 are overlappedwith each other. Then, it becomes a problem how to overlap the endportions 1 a of the linear laser beams 1. In FIG. 13(B), a region 4shown in a rectangle is a region where scanning is performed by theoverlapped end portions 1 a of the linear laser beams 1 in the surfaceto be irradiated.

[0016] However, in general, since it is difficult to control the energydensity at the end portion 1 a of the linear laser beam 1, semiconductordevices formed in the region 4 and in the neighborhood thereof are ofextremely uneven characteristics as compared with devices formed inother region. Thus, the semiconductor material in the region 4 is notsuitable for processing of semiconductor devices.

[0017] As a countermeasure to the above problem, by irradiation of alaser beam through a slit, the end portion in the longitudinal directionin which the control of energy density is difficult, is shielded toshape the end portion of the laser beam. FIG. 14(A) is a sectional viewshowing a linear laser beam shaped by the slit, and FIG. 14(B) is aschematic view showing scanning paths of the laser beam and is a viewshowing a surface to be irradiated viewed from the above.

[0018] As shown in FIG. 14(A), through the slit, an end portion 5 a of alaser beam 5 is shaped into a rectangle, so that the distribution of theenergy density in the end portion 5 a becomes uniform than the linearlaser beam 1 shown in FIG. 13 (A) As shown in FIG. 14(B), when theirradiation of the linear laser beam 5 is performed, for example, thefollowing scanning steps may be made: after the downward scanning of thelinear laser beam 5 is performed along a left scanning path 6, thedownward scanning is performed along a right scanning path 7. At thistime, the scanning is performed so that the end portions 5 a of thelinear laser beams 5 are overlapped with each other. However, since theend portion 5 a of the laser beam 5 is shaped into a rectangle, and theenergy density distribution is uniform, it is sufficient to overlap theend portions 5 a of the linear laser beam 5 with each other to theextent that the end portions 5 a are brought into contact with eachother, as shown by reference numeral 8. Thus, it is possible to reducethe region 8 where the ends 5 a are overlapped with each other.

[0019] However, even if the energy density in the end portion 5 a of thelaser beam 5 is controlled by using the slit, the semiconductor devicesformed in the region 8 to be scanned with the overlapped end portions 5a of the laser beam 5, are of remarkably uneven characteristics ascompared with devices formed in other region.

[0020] An object of the present invention is to provide a laserprocessing method and a laser processing apparatus that can eliminatethe above-described problems and can perform the steps of laserannealing for a semiconductor film having a large area with highthroughput.

[0021] Another object of the present invention is to provide a laserprocessing method and a laser processing apparatus for a semiconductorfilm having a large area, which can prevent unevenness ofcharacteristics among a plurality of semiconductor devices.

[0022] In order to solve the problems, according to a first aspect ofthe invention, a laser processing method is characterized in that when asemiconductor film, a width of which is longer than a length of thecross-section of a laser beam, is scanned and irradiated with the laserbeam having the linear cross section to perform annealing, asemiconductor device is not formed in a region irradiated with endportions of the laser beams in a longitudinal direction thereof whichare overlapped with each other or brought into contact with each other.

[0023] According to a second aspect of the invention, a laser processingmethod is characterized by comprising the steps of: repeatedly scanningand irradiating a semiconductor film on a substrate with a laser beamhaving a linear cross section; wherein the semiconductor film on thesubstrate includes a plurality of device regions separated from oneanother; and wherein the semiconductor film is scanned with the laserbeam in such a manner that a region irradiated with end portions of thelaser beams in a longitudinal direction thereof, which are overlappedwith each other, is positioned outside the device regions.

[0024] According to a third aspect of the invention, a laser processingmethod in which a semiconductor film on a substrate is scanned andirradiated with a laser beam having a linear cross section, a length ofthe cross section of the linear laser beam being shorter than alargeness of a device region of the semiconductor region, the method ischaracterized by comprising the steps of cutting an end portion of thelinear laser beam in a longitudinal direction thereof by the irradiationof the linear laser beam to the semiconductor film through a slit; laserprocessing one portion of the device region through scanning of thelinear laser beam to form a laser-processed portion; and laserprocessing a non-laser-processed portion in the device region with a newlinear laser beam passing through the slit in such a manner that an endof the laser beam in a longitudinal direction thereof with which thelaser-processed portion has been scanned, is brought into contact withan end of the new laser beam in a longitudinal direction thereof.

[0025] According to a fourth aspect of the invention, a laser processingmethod in which a semiconductor film on a substrate is scanned andirradiated with a laser beam having a linear cross section, a length ofthe cross section of the linear laser beam being shorter than alargeness of a device region of the semiconductor region, the method ischaracterized by comprising the steps of: laser processing one portionof the device region by scanning and irradiating the semiconductor filmwith the linear laser beam to form a laser-processed portion, an endportion of the linear laser beam in a longitudinal direction thereofbeing cut through a slit; and laser processing a non-laser-processedportion in the device region with a new linear laser beam passingthrough the slit in such a manner that an end of the laser beam in alongitudinal direction thereof with which the laser-processed portionhas been scanned, is overlapped with an end of the new laser beam in alongitudinal direction thereof by a range of 10 to 20 μm.

[0026] According to a fifth aspect of the invention, a laser processingmethod in which a semiconductor film on a substrate is scanned andirradiated with a laser beam having a linear cross section, a length ofthe cross section of the linear laser beam being shorter than alargeness of a device region of the semiconductor region, the method ischaracterized by comprising the steps of cutting an end portion of thelinear laser beam in a longitudinal direction thereof by the irradiationof the linear laser beam to the semiconductor film through a slit; laserprocessing one portion of the device region through scanning of thelinear laser beam to form a laser-processed portion; and laserprocessing a non-laser-processed portion in the device region with a newlinear laser beam passing through the slit in such a manner that an endof the laser beam in a longitudinal direction thereof with which thelaser-processed portion has been scanned, is brought into contact withan end of the new laser beam in a longitudinal direction thereof,wherein a semiconductor device is not provided in a subsequent step at aposition where the end portions are brought into contact with eachother.

[0027] According to a sixth aspect of the invention, a laser processingmethod in which a semiconductor film on a substrate is scanned andirradiated with a laser beam having a linear cross section, a length ofthe cross section of the linear laser beam being shorter than alargeness of a device region of the semiconductor region, the method ischaracterized by comprising: laser processing one portion of the deviceregion by scanning and irradiating the semiconductor film with thelinear laser beam to form a laser-processed portion, an end portion ofthe linear laser beam in a longitudinal direction thereof being cutthrough a slit; and laser processing a non-laser-processed portion inthe device region with a new linear laser beam passing through the slitin such a manner that an end of the laser beam in a longitudinaldirection thereof with which the laser-processed portion has beenscanned, is overlapped with an end of the new laser beam in alongitudinal direction thereof by a range of 10 to 20 μm, wherein asemiconductor device is not provided in a subsequent step at a positionwhere the end portions are overlapped with each other.

[0028] According to a seventh aspect of the invention, a laserprocessing method of any one of the first to sixth aspects ischaracterized in that the substrate constitutes a liquid crystaldisplay.

[0029] According to the present invention, when a semiconductor filmhaving a width longer than a cross section of a laser beam is scannedand irradiated with the linear laser beam to perform annealing, asemiconductor device is not formed in a region irradiated with endportions 1 a, 5 a of the laser beams 1,5, as shown in FIG. 12, which areoverlapped with each other.

[0030] In other words, laser irradiation is controlled in such mannerthat a region irradiated with end portions of the laser beams in thelongitudinal direction thereof which are overlapped with each other orbrought into contact with each other, is not positioned on a deviceregion of the semiconductor film (where a semiconductor device isprovided).

[0031] According to this method, even if a substrate becomes large and aregion to be irradiated becomes large, laser annealing can be performedwith a high throughput, and variation of characteristics amongsemiconductor devices can be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032]FIG. 1 is a construction view of a laser irradiation apparatus ofa first embodiment and is also a top view;

[0033]FIG. 2 is a sectional view taken along line A-A′ in FIG. 1;

[0034]FIG. 3 is a sectional view taken along line B-B′ in FIG. 1;

[0035]FIG. 4 is a construction view showing laser irradiating means 39;

[0036]FIG. 5 is a construction view showing a lens system;

[0037]FIG. 6 is a construction view of a lens system and is also asectional view along a light path in FIG. 5;

[0038] FIGS. 7(A) to 7(C) are explanatory views showing forming steps ofa crystalline silicon film in a second embodiment;

[0039] FIGS. 8(A) to 8(E) are explanatory views of scanning paths of alaser beam;

[0040]FIG. 9 is an explanatory view of division of a substrate;

[0041] FIGS. 10(A) to 10(D) are explanatory views showing forming stepsof a TFT in a third embodiment;

[0042] FIGS. 11(A) to 11(C) are explanatory views showing forming stepsof a TFT in a third embodiment;

[0043] FIGS. 12(A) to 12(C) are explanatory views of scanning paths of alaser beam in a fifth embodiment;

[0044] FIGS. 13(A) and 13(B) are explanatory views showing the shape ofa conventional laser beam and a scanning method; and

[0045] FIGS. 14(A) and 14(B) are explanatory views showing the shape ofa conventional laser beam and a scanning method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046] Preferred embodiments of the present invention will be describedwith reference to the accompanying drawings.

[0047] [First Embodiment]

[0048] FIGS. 1 to 3 are construction views showing a laser irradiationapparatus of the first embodiment, in which FIG. 1 is a too view, FIG. 2is a sectional view taken along dotted line A-A′ in FIG. 1, and FIG. 3is a sectional view taken along dotted line B-B′ in FIG. 1. The laserirradiation apparatus of this embodiment is an apparatus ofmulti-chamber type, and also a single wafer processing apparatus thatcan process a plurality of substrates (test pieces) continuously one byone.

[0049] A plurality of substrates 10 to be processed are contained in acartridge 11, and the substrates together with the cartridge 11 arecarried into the apparatus.

[0050] A cartridge carry-in and carry-out chamber 17, a heating chamber18, and a laser irradiation chamber 19 are respectively connected bygate valves 14 to 16 to a substrate transport chamber 13 fortransporting the substrates 10 in the apparatus. The substrate transportchamber 13, the cartridge carry-in and carry-out chamber 17, the heatingchamber 18, and the laser irradiation chamber 19 can be kept airtight,upper portions of which are respectively connected to gas supply systems20 to 23 for supplying a gas, an inert gas and the like, and lowerportions of which are respectively connected to exhaust systems 29 to 32connected with vacuum pumps 25 to 28. By this structure, atmospheres,pressures and the like in the substrate transport chamber 13, thecartridge carry-in and carry-out chamber 17, the heating chamber 18, andthe laser irradiation chamber 19 can be controlled.

[0051] A robot arm 33 is provided in the substrate transport chamber 13,so that the substrates 10 can be transported into the cartridge carry-inand carry-out chamber 17, the heating chamber 18, or the laserirradiation chamber 19 one by one. Further, an alignment mechanism 34 isprovided at the side of the gate valve, so that positioning-of thesubstrate 10 and the robot arm 33 is carried out.

[0052] In the heating chamber 18, a plurality of substrates 10 can becontained on an elevator 35, and the substrates 10 are heated up to apredetermined temperature by heating means 36 formed of resistors andthe like.

[0053] Further, in the laser irradiation chamber 19, a stage 37 on whichthe substrates 10 are set, is provided. The stage 37 includes heatingmeans for heating the substrates 10, is freely and horizontally moved inthe two-dimensional direction in the paper surface of FIG. 1 by a guidemechanism, motor and the like not shown, and is freely rotated around anaxis orthogonal to the paper surface. Further, a quartz window 38 onwhich laser light emitted from the outside of the apparatus is madeincident, is provided on the upper surface of the laser irradiationchamber 19.

[0054] As shown in FIG. 2, laser irradiation means 39 is provided in theoutside of the apparatus, a mirror 40 is arranged on an optical path 41of the laser light of the laser irradiating means 39 in the emittingdirection, and the quartz window 38 of the laser irradiation chamber 19is provided on the optical path 41 bent by the mirror 40. The laserlight emitted from the laser irradiation means 39 is reflected by themirror 40, passes through the quartz window 38, and is made incident onthe substrate 10 arranged or the stage 37.

[0055]FIG. 4 is a schematic construction view showing the laserirradiation means 39. Total reflection mirrors 52 and 53 are arranged onan optical path 50 of an oscillator 51, which generates the laser light,in the emitting direction thereof. On the optical path 50 in thereflection direction of the total reflection mirror 53, an amplifier 54,an attenuation means 55 formed of a plurality of filters 55 a to 54 d,and an optical system 56 for shaping the laser light into a linear beamare sequentially arranged.

[0056] The attenuation means 55 is for adjusting the laser energy. Thefilters 55 a to 55 d have a function to attenuate the energy oftransmitted light. Transmissivities of these filters are different fromone another. In this embodiment, the transmissivities of the filters 55a to 55 d are respectively 96%, 92%, 85%, and 77%. These filters 55 a to55 d are independently taken into and out of the optical path 50 bydriving means such as an electromagnet or a motor not shown. By suitablycombining the filters 55 a to 55 d, a filter with transmissivity of 57to 96% can be formed. For example, by combining the filter 55 a oftransmissivity of 96% and the light reduction filter 55 b oftransmissivity of 92%, a light reduction filter of transmissivity of 88%can be obtained.

[0057] The filters 55 a to 55 d are made of quartz coated with layers ofhafnium oxide and silicon dioxide alternatively laminated. Thetransmissivity of the light reduction filters 55 a to 55 d depends onthe number of coated layers. In this embodiment, although the number ofthe filters 55 a to 55 d of the attenuation means 55 is four, theinvention is not limited to this number, but the number, transmissivityand the like of the filters may be determined so that the laser energycan be suitably adjusted.

[0058]FIGS. 5 and 6 are construction views showing the optical system56, and FIG. 6 corresponds to a sectional view along the optical path 50in FIG. 5. As shown in FIGS. 5 and 6, on the optical path 50, acylindrical concave lens 61, a cylindrical convex lens 62, fly eyelenses 63 and 64 having axes orthogonal to each other, cylindricalconvex lenses 65 and 66, and a total reflection mirror 67 are arrangedsequentially from the incident direction. A cylindrical lens 68 isarranged on an optical path in the reflection direction of the totalreflection mirror 67.

[0059] In the laser irradiation means 39 shown in FIG. 4, the laserlight oscillated by the oscillator 51 is reflected by the totalreflection mirrors 52 and 53, and made incident on the amplifier 54. Inthe amplifier 54, the laser light is amplified, reflected by the totalreflection mirrors 52 and 53 respectively, passes through theattenuation means 55, and reaches the optical system 56. As shown inFIGS. 5 and 6, the laser light passes through the cylindrical concavelens 61, the cylindrical convex lens 62, and the fly eye lenses 63 and64, so that the energy distribution of the laser light is changed fromthe Gaussian distribution type to the rectangular distribution type.Further, the laser light passes through the cylindrical convex lenses 65and 66, reflected bay the total reflection mirror 67, and collected bythe cylindrical lens 63, so that a linear beam image is made on focalsurface f. This linear beam image has its longitudinal directionvertical to the paper surface in FIG. 6.

[0060] The shape of the laser beam immediately before being madeincident on the optical system 56 is a rectangle of 3×2 cm². However,after the laser beam passes through the optical system 56, the beam isshaped into a thin and long linear beam with a length of 10 to 30 cm anda width of about 0.1 to 1 cm.

[0061] In the case where laser annealing is performed by using the laserirradiation apparatus shown in FIGS. 1 to 3, the gate valves 14 to 16are first closed, and the substrate transport chamber 13, the heatingchamber 18, and the laser irradiation chamber 19 are filled with anitrogen gas.

[0062] Next, the cartridge 11 containing a plurality of substrates 10 iscarried in the cartridge carry-in and carry-out chamber 17 from theoutside. In the cartridge carry-in and carry-out chamber 17, a door notshown is provided. By closing and opening this door, the cartridge 11 iscarried in and carried out. After the cartridge 11 is carried in thecartridge carry-in and carry-out chamber 17, the door is closed to sealthe cartridge carry-in and carry-out chamber 17, and the nitrogen gas issupplied from the gas supply system 21 to fill the cartridge carry-inand carry-out chamber 17 with the nitrogen gas. The pressure in thecartridge carry-in and carry-out chamber 17 is not specifically reduced,but kept at an atmospheric pressure. Next, the gate valve 14 and thegate valve 15 are opened. The gate valve 14 may be kept open until aseries of steps are ended.

[0063] By the robot arm 33, the substrates 10 are taken from thecartridge 11 set in the cartridge carry-in and carry-out chamber 17 oneby one, and are mounted on the alignment mechanism 34. After the robotarm 33 and the substrate 10 are once positioned, the substrate 10 isagain taken by the robot arm 33, and transported into the heatingchamber 18. At each time when the substrates 10 are transported into theheating chamber 18, the elevator 35 rises or falls so that thesubstrates 10 are contained in the sequentially laminated state.

[0064] After a predetermined number of substrates 10 are transportedinto the heating chamber 18, the gate valve 15 is closed, and thesubstrates 10 are heated by the heating means 36. When the substrates 10are heated to a predetermined temperature, the gate valve 15 is opened,the substrates 10 are transported to the substrate transport chamber 13from the heating chamber 18 by the robot arm 33, set on the alignmentmechanism 34, and again positioned.

[0065] After the gate valve 16 is opened, the substrate 10 on thealignment mechanism 34 is set on the stage 37 in the laser irradiationchamber 19 by the robot arm 33, then the gate valve 15 and the gatevalve 16 are closed. It is preferable that the gate valve 15 is openedand closed at each time when the transport of the substrate isperformed. This is because it is preferable to prevent the atmosphere inthe heating chamber 18 from exerting thermal affection to the mechanicalstructure such as the robot arm 33.

[0066] After the gate valve 16 is closed, the linear laser beam isemitted from the laser irradiation means 39, and the linear laser beamis made incident on the substrate 10 on the stage 37 through the mirror40 and the quartz window 38. The linear laser beam is made incident onthe substrate 10 along the predetermined scanning path by rotating andhorizontally moving the stage 37. During the irradiation of the laserbeam, the substrate 10 is heated to the same temperature as atemperature in the heating chamber 18 by the heating means provided inthe stage 37, so that thermal variation is suppressed. When theirradiation of the laser beam is ended, the gate valve 16 is opened, andthe substrate 10 is contained in the cartridge 11 in the cartridgecarry-in and carry-out chamber 17 by the robot arm 33. In this way, theprocess for one substrate 10 is ended.

[0067] When the process for one substrate 10 is ended, the gate valve 15is opened, the following substrate 10 is taken from the heating chamber18 by the robot arm 33, transported into the laser radiation chamber 19,set on the stage 37, and irradiated with the laser beam. In this way,the substrates 10 contained in the heating chamber 18 are irradiatedwith the laser beam one by one. When all steps are ended, all substrates10 to have been processed are contained in the cartridge 11 set in thecartridge carry-in and carry-out chamber 17. This cartridge 11 is takenfrom the cartridge chamber 17, and the process may proceed with a nextstep.

[0068] It is necessary that the heating temperature in the heatingchamber 18 is made lower than a temperature at which the amorphoussilicon film is crystallized. This is because time intervals in whichthe substrates 10 are in the heating chamber, are different from eachother. In general, the heating temperature in the heating chamber 18 isselected to be about 200 to 400° C. Further, it is necessary that thisheating temperature is made the same as a heating temperature or thesubstrate 10 at the irradiation of the laser light.

[0069] [Second Embodiment]

[0070] In this embodiment, there is shown a case where a substratehaving a size exceeding a linear laser beam is used, and the crystallinesilicon film for manufacturing a semiconductor device is formed. FIGS.7(A) to 7(C) are views showing manufacturing steps of the crystallinesilicon film.

[0071] As shown in FIG. 7(A), on a glass substrate 71 (in thisembodiment, Corning 7059 of 360 mm×460 mm is used), a silicon oxide filmas an under film 72 of a thickness of 2000 Å, and an amorphous siliconfilm 73 of a thickness of 500 Å are continuously formed by a plasma CVDmethod.

[0072] Then, a nickel acetate solution of 10 ppm is coated on thesurface of the amorphous silicon film 73 by a spin coat method, and thesurface is dried to form a nickel layer 74. When a surface active agentwas added into the nickel acetate solution, a better result wasobtained. Since the nickel layer 74 is very thin, it is not necessarilya film. However, there is no problem in the subsequent steps.

[0073] As shown in FIG. 7(B), the amorphous silicon film 73 is annealedat 550° C. for four hours to crystallize the amorphous silicon film, sothat the crystalline silicon film 75 is obtained. By heating, the nickelin the nickel layer 74 functions as nuclei of crystal so thatcrystallization of the amorphous silicon film 73 is accelerated. Thus,the crystalline silicon film 75 can be obtained at a low temperaturesuch as 550° C. (less than a distortion temperature of Corning 7059) andfor a short time such as four hours.

[0074] It was preferable that the concentration of catalytic element inthe crystalline silicon film 75 was 1×10¹⁵ to 1×10¹⁹ atom/cm³ If theconcentration is less than 1×10¹⁵ atom/cm³, it is difficult to obtainthe catalytic effect to accelerate the crystallization. If theconcentration is higher than 1×10¹⁹ atom/cm³, metallic characteristicsappear in the silicon, so that semiconductive characteristics disappear.In this embodiment, the minimum value of the concentration of thecatalytic element in the crystalline silicon film 75 was 1×10¹⁷ to5×10¹⁸ atom/cm³. These values were analyzed and measured by a secondaryion mass spectroscopy (SIMS).

[0075] In order to further improve the crystallinity of the thusobtained crystalline silicon film 75, as shown in FIG. 7(C), the film 75is irradiated with an excimer laser of a large power pulse laser to formthe crystalline silicon film 76 having superior crystalline properties.

[0076] When the irradiation of a laser beam is performed, using theapparatus as shown in FIGS. 1 to 6, a KrF excimer laser beam (wavelength248 nm, pulse width 30 nsec) is shaped into a linear beam of 1 mm×185mm, the irradiation of the laser beam with the energy density of about220 mJ/cm² is first performed, and then the irradiation of the laserbeam with the energy density within the range of 100 mJ/cm² to 500mJ/cm², for example, with the energy density of 370 mJ/cm² is performed.Also, when attention is paid to one point of a material to beirradiated, the scanning speed of the laser beam, actually the movingspeed of the stage 37 on which the substrate 71 is set, is adjusted sothat the irradiation of 2 to 20 shots of the laser beam is performed.

[0077] The change of the laser energy from 220 mJ/cm² to 370 mJ/cm² iscarried out in such a manner that in the laser irradiation means 39shown in FIG. 4, the filters 55 a to 55 d of the attenuation means 55are selectively inserted into and retracted from the optical path 50 inthe state in which the output of the oscillator 51 is kept constant. Thesubstrate temperature at the laser irradiation is 200° C.

[0078] It is assumed that such an irradiating method with changedirradiation energies is referred to as multi-stage irradiation. In thisembodiment, irradiation is performed twice, so that two-stageirradiation is performed. By the two-stage irradiation, thecrystallinity of the crystalline silicon film 76 can be further improvedthan one-stage irradiation. In case of the one-stage irradiation, theirradiation of the laser beam with the energy density within the rangeof 100 mJ/cm² to 500 mJ/cm², for example, with the energy density of 370mJ/cm² may be performed.

[0079] FIGS. 8(A) to 8(D) show scanning paths of the laser beam in thisembodiment. As shown in FIGS. 8(A) to 8(D), on the surface of thesubstrate 80 to be irradiated, rectangular device-formation regions 81on which thin-film transistors are formed, are arranged in the matrix of2×2. Thus, on the glass substrate 71 shown in FIG. 7(C), semiconductordevices are formed by using only the crystalline silicon 76 in thedevice-formation region 81. The substrate 80 on which semiconductordevices are formed, are divided into four device-substrates 86A to 86Das shown in FIG. 9.

[0080] Also, as shown in FIG. 9, it is presumed that a semiconductordevices are formed, the substrate 80 is divided into pieces having alength shorter than the length of the linear laser beam. Thus, in orderto achieve the state that the region 4 or 8 shown in FIG. 13(B) or14(B), which is irradiated with the overlapped end portions of the laserbeams in the longitudinal direction thereof, are positioned outside thedevice formation region 81, length L of the linear laser beam 82 in thelongitudinal direction is made longer than width W of thedevice-formation region 81.

[0081] In order to achieve the two-stage irradiation, as shown in FIGS.8(A) to 8(C), scanning paths 83 a to 83 c are set to be parallel and todraw one continuous line so that the device-formation regions 81 aretwice irradiated with the linear laser beam 82. When one-stageirradiation is performed, as shown in FIG. 8(D), for example, thescanning path 85 may be set. The scanning paths 83 a to 83 c, and 85 aremade in uniform direction for all device-formation regions 80 on thesame substrate 80.

[0082] In order to make scanning of the linear laser beam 83 along thescanning paths as shown in FIGS. 8(A) to 8(C) or 8(D), the irradiationof the linear laser beam 82 may be performed while the linear laser beamis moved along the direction substantially orthogonal to thelongitudinal direction of the beam and relatively to the surface 80 tobe irradiated. Actually, the laser beam 82 is not moved but the stage 37is rotated and moved horizontally in the laser irradiation apparatusshown in FIGS. 1 to 3, so that the substrate having the surface 80 to beirradiated is moved and the scanning of the linear laser beam 82 alongthe scanning path 83 a, 83 b, or 83 c is performed.

[0083] In this embodiment, since the width W of the device-formationregion 81 is shorter than length L of the linear laser beam 82, thedevice-formation region 81 is not scanned with the end portion of thelinear laser beam 82. Accordingly, the film quality of the thus obtainedcrystalline silicon film 76 can be made uniform, so that thecharacteristics of semiconductor devices formed in the device-formationregions 81 can be made uniform. Further, since many substrates on whichsemiconductor devices having the same characteristics are formed, can beproduced by one step by processing the substrate 80 with a large area,the throughput can be improved.

[0084] [Third Embodiment]

[0085] In this embodiment, using the crystalline silicon film 76obtained in the second embodiment, steps of forming a thin-filmtransistor for driving picture elements of a liquid crystal displaydevice will be described. FIGS. 10(A) to 10(D) and 11(A) to 11(C) showmanufacturing steps of the thin-film transistor of this embodiment.

[0086] As shown in FIG. 10(A), a silicon oxide film with a thickness of3000 Å as an under film 102 is deposited by a plasma CVD method or a lowpressure thermal CVD method on a glass substrate 101, and a crystallinesilicon film 103 made of a crystallized amorphous silicon film inaccordance with the crystallization steps shown in the secondembodiment, is formed on the surface of the under film 102.

[0087] Next, as shown in FIG. 10(B), the crystalline silicon film 103 isetched into island-like portions, so that a plurality of active layers104 are formed at predetermined positions in a device-formation region100. In this embodiment, as shown in FIGS. 8(A) to 8(D) and 9, since anobject is to provide four device-substrates with the samecharacteristics by dividing the glass substrate 101 into four pieces,the rectangular device-formation regions 100 on which thin-filmtransistors are formed, are arranged on the glass substrate 101 in thematrix of 2×2. A plurality of active layers 104 are formed atpredetermined positions in the device-formation region 100. Thus, whenthe crystalline silicon film 103 is obtained, the end portion of thelinear laser beam is made not to pass through the inside of thedevice-formation region 100. Next, a silicon oxide film 105 constitutinga gate insulating film and having a thickness of 1000 to 1500 Å isformed by the plasma CVD method, and an aluminum film constituting agate electrode 106 and having a thickness of 5000 Å is deposited by asputtering method. If scandium of 0.2 weight % is mixed in the aluminumin advance, it is possible to prevent generation of hillock or whiskersin the subsequent heating steps.

[0088] Next, the surface of the aluminum film is subjected to anodicoxidation, so that fine anodic oxidation material not shown is formedinto a very thin film. Next, a mask 107 of a resist is formed on thesurface of the aluminum film. At this time, since the fine anodicoxidation material not shown is formed on the surface of the aluminumfilm, it is possible to form the mask 107 of the resist brought intoclose contact. Then, using the mask 107 of the resist, the aluminum filmis etched to form the gate electrode 106.

[0089] As shown in FIG. 10(C), while the mask 107 of the resist remains,the gate electrode 106 is subjected to anodic oxidation to form porousanodic oxidation material 108 with a thickness of 4000 Å. At this time,since the mask 107 of the resist is brought into close contact with thesurface of the gate electrode 106, the porous anodic oxidation material108 is formed only on the side of the gate electrode 106.

[0090] Next, as shown in FIG. 10(D), after the mask 107 of the resist ispeeled off, the gate electrode 106 is again subjected to the anodicoxidation in an electrolytic solution to form fine anodic oxidationmaterial 109 with a thickness of 1000 Å.

[0091] The anodic oxidation materials can be changed by changing thesolution used. In the case where the porous anodic oxidation material108 is formed, an acid solution including citric acid, oxalic acid,chromic acid, or sulfuric acid of 3 to 20% may be used. On the otherhand, in the case where the fine positive anodic oxidation material 109is formed, an electrolytic solution made of an ethylene glycol solutionwhich includes tartaric acid, boric acid, or nitric acid of 3 to 10% andPH of which is adjusted to about 7, may be used.

[0092] As shown in FIG. 11(A), with the mask of the gate electrode 106,the porous anodic oxidation material 103 around the gate electrode, andthe fine anodic oxidation material 109, the silicon oxide film 105 isetched to form the gate insulating film 110.

[0093] As shown in FIG. 11(B), after the porous anodic oxidationmaterial 108 is removed, by an ion doping method, impurities areinjected into the active layer 104 with the mask of the gate electrode106, the fine anodic oxidation material 109, and the gate insulatingfilm 110. In this embodiment, in order to form a P-channel TFT,phosphine (PH₃) is used as a doping gas, so that phosphorus ions aredoped. At the doping, conditions such as a dose amount and accelerationvoltage are controlled so that the gate insulating film 110 functions asa semi-transparent mask.

[0094] As a result of doping, the phosphorus ions in high concentrationare injected into regions not covered with the gate insulating film 110,so that a source region 111 and a drain region 112 are formed. Thephosphorus ions in low concentration is injected into regions coveredwith only the gate insulating film 110, so that regions 113 and 114 withlow concentration impurity are formed. Since impurities are not injectedinto regions immediately under the gate electrode 106, a channel region115 is formed.

[0095] Since the region 113 and 114 with low concentration impurityfunction as high resistance regions, they contributes to reduction of anoff-current. Especially, the low concentration impurity region 113 atthe side of the drain region 112 is referred to as LDD. Further, bysufficiently increasing the thickness of the fine anodic oxidationmaterial 109, the region immediately under the fine anodic oxidationmaterial 109 is made into an offset region, so that the off-current canbe reduced further.

[0096] After the doping step, in the laser irradiation apparatus shownin FIGS. 1 to 3, the laser annealing is performed, so that the dopedphosphorus ions are activated. The annealing conditions in this case aresuch that the energy density of the laser is within the range of 100mJ/cm² to 350 mJ/cm², for example, 160 mJ/cm², the irradiation of 20 to40 shots of the linear laser beams is performed when attention is paidto an arbitrary point on the surface to be irradiated, and the substratetemperature is kept at 200° C. Since one-stage irradiation is performed,the scanning of the linear laser beam may be performed along thescanning path 85 shown in FIG. 8(D). At this time, the end portion ofthe linear laser beam is made not to pass through the device-formationregion 100.

[0097] After the laser annealing, the thermal annealing ray beperformed. In this case, heating at a temperature of 450° C. and for twohours may be performed.

[0098] As shown in FIG. 11(C), by the plasma CVD method, a silicon oxidefilm with a thickness of 5000 Å as an interlayer insulator 116, isformed. As the interlayer insulator 116, a single layer film of siliconnitride film, or a laminated film of silicon oxide film and siliconnitride film may be formed instead of the single layer film of siliconoxide film. Next, by a well-known etching method, the interlayerinsulator 116 made of the silicon oxide film is etched, so that contactholes are respectively formed in the source region 111 and the drainregion 112.

[0099] Next, an aluminum film with a thickness of 4000 Å is formed by asputtering method, which is patterned to form electrodes 117 and 118connected to the source region 111 and the drain region 112. A siliconnitride film as a passivation film 119 is formed, and a contact hole forelectrode 118 at the side of the drain region 112 is formed in thepassivation film 119. Next, an ITO film is formed and patterned so thata picture element electrode 120 is formed in the contact hole connectedto the electrode.

[0100] After the above-described steps, the TFT having the LDD structureis formed in the device-formation region 100 on the glass substrate 101.Lastly, the substrate 101 is divided for each device-formation region100 as shown in FIG. 9, so that four pieces of panels for the liquidcrystal display device can be obtained.

[0101] In this embodiment, manufacturing steps of N-channel thin-filmtransistor for driving picture elements of the liquid crystal displaydevice have been explained. However, a thin-film transistor constitutinga peripheral driving circuit and a thin-film transistor for drivingpicture elements may be formed in one device-formation region 100 at thesame time. In this case, the conductivity of the thin-film transistormay be controlled by using a well-known CMOS technique so that thethin-film transistor constituting the peripheral driving circuit becomesa complementary thin-film transistor composed of an N-channel thin filmtransistor and a P-channel thin-film transistor.

[0102] [Fourth Embodiment]

[0103] This embodiment relates to a scanning path of a laser beam in thecase where a substrate is not divided. In this case, there is thepossibility that the region 4 in which end portions of a linear laserbeam are overlapped with each other as sown in FIG. 13(B), or the region8 where the end portions are brought into contact with each other asshown. In FIG. 14(2), is arranged in the device-formation region. Inthis case, semiconductor devices are arranged so that the semiconductordevices do not extend over (is not positioned at, is not positionednear) the region 4 or 8 shown in FIG. 13 (B) or 14(B).

[0104] For example, in FIGS. 10(A) to 10(D), in order not to make theactive layer 104 of the thin-film transistor and the region 4 or 8overlap with each other, the length of the linear beam may be adjustedso that the end portion of the laser beam passes through a region 200where the active layer 104 is not formed.

[0105] Depending on the density of the semiconductor devices on thesubstrate, it is determined whether the portion (joint portion)irradiated with the overlapped ends of the linear laser beams is made aportion like the region 4 in FIG. 13 where the end portions of the laserbeams are overlapped to some extent, or a portion like the region 8 inFIG. 14 where the end portions are brought into contact with each other.

[0106] If the interval between semiconductor devices is the order ofmillimeter, the shape of the end portion of the linear laser beam, thatis, the distribution of energy density at tine end portion does notbecome a problem. Accordingly, as shouts in FIG. 13(A), it is possibleto perform the irradiation of the linear laser beam without shaping theend portion 1 a of the linear laser beam 1. However, if the intervalbetween semiconductor devices is less than the order of millimeter, itis necessary to shape the linear laser beam by a slit to make therectangle end portion as shown in FIG. 14(A), and further to makescanning so that the end portions of the linear laser beam is broughtinto contact with each other as shown in FIG. 14(B).

[0107] Further, if the interval between the semiconductor devicesbecomes the order of micron, even if the scanning of the linear laserbeam is performed as shown in FIG. 14(B), due to the limit of accuracyin alignment or the like in the process, there is a fear that a deviceis formed in the region 8 where the end portion 5 a of the laser beam 5passes. That is, it is difficult to form a device in a region where theend portion 5 a of the laser beam 5 does not pass.

[0108] In the case where as a semiconductor device, for example, a panelof a liquid crystal display is formed, the interval at which thin-filmtransistors as semiconductor devices formed on the substrate is about 10μm to 100 μm. Thus, in this case, using the slit, the end portion of thelinear laser beam in the longitudinal direction thereof is cut, and thescanning of the linear laser beam is performed so that the jointportions of the linear laser beam, that is, the end portions of the beamare brought into contact with each other. In this case, if the jointportions are brought into close contact with each other by the accuracyof about 10 to 20 μm, the accuracy is sufficient. It is possible to forma panel for a liquid crystal display without forming semiconductordevices on the joint portion.

[0109] [Fifth Embodiment]

[0110] As shown in FIGS. 8(A) to 8(D), in the second embodiment, thedevice-formation regions 80 are arranged on the substrate 80 in thematrix of 2×2. In order to make the device-formation regions irradiateduniformly with the laser beam, it is preferable to arrange thedevice-formation regions symmetrically with respect to the substrate.Thus, the regions are preferably arranged in the matrix of 2n×2n (n isnatural numbers more than one). In this embodiment, as shown in FIGS.12(A) and 12(B), by using a substrate with a larger area, thedevice-formation regions 91 of 4×4 are arranged on the substrate, sothat by one step, sixteen pieces of substrates on which semiconductordevices having the same characteristics can be obtained from the onesubstrate 90.

[0111] In order to perform the two-stage irradiation of the linear laserbeam 92, for example, as shown in FIGS. 12(A) and 12(B), the scanningpaths 93A and 93B may be set. Further, in order to perform uniformscanning of the linear laser beam 93, the length L of the linear laserbeam 92 in the longitudinal direction thereof is made loner than thewidth W of the device-formation region 91, and the region irradiatedwith the overlapped end portions of the laser beam 92 in thelongitudinal direction thereof is made the outside of thedevice-formation region 91.

[0112] As described above, according to the present invention, it ispossible to perform the step of laser annealing or a semiconductormaterial having a large area with a high throughput. Further, accordingto the present invention, it is possible to suppress variation incharacteristics among a plurality of semiconductor devices formed by thelaser annealing process for a semiconductor film with a large area.

[0113] The present invention is specifically effective in the case wheremany TFTs are formed on the glass substrate with a large area over thewidth of the linear laser beam. Especially, when the substrate is forconstructing a liquid crystal display, it is expected that a largepicture surface is required, and the present invention can make such alarge surface. Thus, the present invention is useful in technology.

What is claimed is:
 1. A method of manufacturing a display devicecomprising: forming a semiconductor film over a substrate; generating alaser light form an oscillator, wherein the laser light passes throughan attenuation means comprising a filter, and passes through an opticalsystem after passing through the attenuation means; and irradiating thesemiconductor film with the laser light passed through the opticalsystem.
 2. A method of manufacturing a display device according to claim1, wherein the laser comprises an excimer laser.
 3. A method ofmanufacturing a display device according to claim 1, wherein the laserlight has a length of 10 cm or more at an irradiation surface.
 4. Amethod of manufacturing a display device according to claim 1, whereinthe optical system comprises a cylindrical lens.
 5. A method ofmanufacturing a display device according to claim 1, wherein the displaydevice is a liquid crystal display device.
 6. A method of manufacturinga display device comprising: forming a semiconductor film over asubstrate; generating a laser light form an oscillator, wherein thelaser light passes through an attenuation means comprising a pluralityof filters, and passes through an optical system after passing throughthe attenuation means; and irradiating the semiconductor film with thelaser light passed through the optical system.
 7. A method ofmanufacturing a display device according to claim 6, wherein the lasercomprises an excimer laser.
 8. A method of manufacturing a displaydevice according to claim 6, wherein the laser light has a length of 10cm or more at an irradiation surface.
 9. A method of manufacturing adisplay device according to claim 6, wherein the optical systemcomprises a cylindrical lens.
 10. A method of manufacturing a displaydevice according to claim 6, wherein the plurality of filters havedifferent transmissivities with each other.
 11. A method ofmanufacturing a display device according to claim 6, wherein the displaydevice is a liquid crystal display device.
 12. A method of manufacturinga display device comprising: forming a semiconductor film over asubstrate; generating a laser light form an oscillator, wherein thelaser light passes through an amplifier, an attenuation means comprisinga filter, and passes through an optical system after passing through theattenuation means; and irradiating the semiconductor film with the laserlight passed through the optical system.
 13. A method of manufacturing adisplay device according to claim 12, wherein the laser comprises anexcimer laser.
 14. A method of manufacturing a display device accordingto claim 12, wherein the laser light has a length of 10 cm or more at anirradiation surface.
 15. A method of manufacturing a display deviceaccording to claim 12, wherein the optical system comprises acylindrical lens.
 16. A method of manufacturing a display deviceaccording to claim 12, wherein the display device is a liquid crystaldisplay device.
 17. A method of manufacturing a display devicecomprising: forming a semiconductor film over a substrate; generating alaser light form an oscillator, wherein the laser light passes throughan attenuation means comprising a plurality of filters, and passesthrough an optical system after passing through the attenuation means;first irradiating the semiconductor film with the laser light passedthrough the optical system; and second irradiating the semiconductorfilm with the laser light after the first irradiating step.
 18. A methodof manufacturing a display device according to claim 17, wherein thelaser comprises an excimer laser.
 19. A method of manufacturing adisplay device according to claim 17, wherein the laser light has alength of 10 cm or more at an irradiation surface.
 20. A method ofmanufacturing a display device according to claim 17, wherein theoptical system comprises a cylindrical lens.
 21. A method ofmanufacturing a display device according to claim 17, wherein theplurality of filters have different transmissivities with each other.22. A method of manufacturing a display device according to claim 17,wherein a same region of the semiconductor film is irradiated by thefirst and the second irradiating steps.
 23. A method of manufacturing adisplay device according to claim 17, wherein the display device is aliquid crystal display device.
 24. A method of manufacturing a displaydevice comprising: forming a semiconductor film over a substrate;generating a laser light form an oscillator, wherein the laser lightpasses through an amplifier, an attenuation means comprising a filter,and passes through an optical system after passing through theattenuation means; and first irradiating the semiconductor film with thelaser light passed through the optical system; and second irradiatingthe semiconductor film with the laser light after the first irradiatingstep.
 25. A method of manufacturing a display device according to claim24, wherein the laser comprises an excimer laser.
 26. A method ofmanufacturing a display device according to claim 24, wherein the laserlight has a length of 10 cm or more at an irradiation surface.
 27. Amethod of manufacturing a display device according to claim 24, whereinthe optical system comprises a cylindrical lens.
 28. A method ofmanufacturing a display device according to claim 24, wherein a sameregion of the semiconductor film is irradiated by the first and thesecond irradiating steps.
 29. A method of manufacturing a display deviceaccording to claim 24, wherein the display device is a liquid crystaldisplay device.
 30. A method of manufacturing a display devicecomprising: forming a semiconductor film over a substrate; generating alaser light form an oscillator, wherein the laser light passes throughan attenuation means comprising a plurality of filters, and passesthrough an optical system after passing through the attenuation means;first irradiating the semiconductor film with the laser light passedthrough the optical system; and second irradiating the semiconductorfilm with the laser light after the first irradiating step, whereindifferent filters are used at each of the first and the secondirradiating step.
 31. A method of manufacturing a display deviceaccording to claim 30, wherein the laser comprises an excimer laser. 32.A method of manufacturing a display device according to claim 30,wherein the laser light has a length of 10 cm or more at an irradiationsurface.
 33. A method of manufacturing a display device according toclaim 30, wherein the optical system comprises a cylindrical lens.
 34. Amethod of manufacturing a display device according to claim 30, whereinthe plurality of filters have different transmissivities with eachother.
 35. A method of manufacturing a display device according to claim30, wherein a same region of the semiconductor film is irradiated by thefirst and the second irradiating steps.
 36. A method of manufacturing adisplay device according to claim 30, wherein the display device is aliquid crystal display device.